Simply put, a magnetosphere is the region where a planet’s magnetic field is dominant. Interplanetary space, on the other hand, is dominated by the Sun’s magnetic field and the solar wind. A strong magnetic field can protect a planet from the solar wind and from coronal mass ejections by deflecting high-energy particles. Mercury, Earth, Jupiter, Saturn, Uranus, and Neptune each have an intrinsic magnetosphere due to their internal magnetic fields. Venus and Mars, on the other hand, lack a global magnetic field, which might have been responsible for Mars losing its atmosphere due to solar wind sputtering.
Today’s Astrobite is an overview of the major features of each magnetosphere. For more detail, the reader is directed to the many links throughout and technical references included at the end.